Scattering of Infrared by Prismatic Cloud Ice Crystals

Cirrus clouds have a large effect in the atmospheric system and radiative budget of earth as they have a huge influence in weather processes and climate in all scales. Cirrus clouds are composed of non-spherical ice crystals with various shapes and cover about 30%-40% globally. The appropriate geometric models (applied mathematics and computational geometry) and incident coordinate systems determine the shapes of ice crystals [1]. The shapes include but not limited to: hollow columns, dendrites, bullet rosettes and capped columns. The scattering solution however in the infrared's part of the spectrum is a complex problem. There are established methods that have been used to solve scattering methods such as Mie, T-matrix and Rayleigh theories. These methods are not efficient at infrared wavelengths due to size parameter, which typically can be in order of 100 or more that leads to intensive computation. In this work, a new approach based on physical optics presented in which the scattering by prismatic dielectric ice crystals which are electrically large is evaluated. In this method, the total scattered amplitude in any direction can be evaluated by application of the reaction theorem to a volume interval in principle from a knowledge of the internal field distribution. This integral in turn can be converted to an integral over the equivalent surface current distribution. The method enables the evaluation of the total surface field by considering the internally transmitted, multiply reflected and diffracted contributions [2], which are obtained by the application of FFT and non-linear rescaling of the spatial frequency domain on each reorder of reflection which meet the boundary conditions [3].